Welcome to the Make Community!
You need to set the “Source Module” field of the aggregator to where the bundles are coming from. This is usually an Iterator module, but can also be a search/list/repeater module, or even your RSS module.
For more information, please refer to the Make Academy.
I highly recommend doing the Make Academy as this is basic scenario flow.
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Investing some effort into the Make Academy will save you lots of time and frustration using Make.